no. R2
A general theorem on triangular finite C (m) -elements
ESAIM: Mathematical Modelling and Numerical Analysis - Modélisation Mathématique et Analyse Numérique, Tome 8 (1974) no. R2, pp. 119-127. 
@article{M2AN_1974__8_2_119_0,
     author = {\v Zen\'\i \v sek, Alexander},
     title = {A general theorem on triangular finite $C^{(m)}$-elements},
     journal = {ESAIM: Mathematical Modelling and Numerical Analysis - Mod\'elisation Math\'ematique et Analyse Num\'erique},
     pages = {119--127},
     publisher = {Dunod},
     volume = {8},
     number = {R2},
     year = {1974},
     zbl = {0321.41003},
     mrnumber = {388731},
     language = {en},
     url = {archive.numdam.org/item/M2AN_1974__8_2_119_0/}
}
Ženíšek, Alexander. A general theorem on triangular finite $C^{(m)}$-elements. ESAIM: Mathematical Modelling and Numerical Analysis - Modélisation Mathématique et Analyse Numérique, Tome 8 (1974) no. R2, pp. 119-127. http://archive.numdam.org/item/M2AN_1974__8_2_119_0/

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